This invention generally relates to torque-transmitting coupling assemblies useful with flexible shafts made of super-elastic alloy, which are particularly beneficial in surgical instrumentation, e.g., flexible reaming systems.
Torque has been traditionally transmitted across non-concentric axes via universal joints. Some have used drive shafts of a coiled spring construction that bend while transmitting torque along a desired path, to ameliorate the surrounding impact of protrusions from such joints. These connections have proven undesirable, particularly in surgical operations. For blood and other organic matter trapped in the assembly cannot easily be cleaned due to the intricate, non-exposed surfaces that are largely inaccessible. Moreover, aspects of universal joints can move against the tissue of a patient to cause a deleterious effect.
One approach has been to utilize flexible tubular shafts made of a super-elastic alloy such as nickel-titanium (e.g., Nitinol) to transmit torque, which has met with some success. Using a tube to transmit torque generally minimizes unexposed surfaces and allows easier cleaning, as there are no surfaces extending beyond the torque transmission tube. Universal joints instead protrude beyond the envelope of the drive shaft. Thus, the use of elastic tubes made of super-elastic alloy in, e.g., surgical devices substantially reduces the possibility of harm or discomfort to a patient.
Unfortunately, prior art devices have coupled tools and other components to a Nitinol tube in such as way as to cause stress risers and notch stresses that increase the possibility of harm to the patient. In the event such stresses cause the tube connection to break, the damage to bone and other body tissue is often catastrophic.
Although others have designed systems that seek to avoid stress risers or notch stresses, these approaches have not resulted in devices that transmit sufficient torque for many orthopedic operations.
Therefore, what is needed is a device that connects to an elastic tube in a manner that does not create stress risers. More specifically, what is needed is a reliable means of connecting various types of tool heads to an elastic tube such that significant torque may be transmitted without raising internal stresses to dangerous levels.
According to the invention, a torque-transmitting assembly is described. A female coupling member defines a shape with a tapered bore. A radially flexible sleeve member has a wall with a tapered exterior surface, received within the bore, and an inner surface defining a through-bore. An elongated shaft member made of super-elastic alloy has an outer surface that is received within the through-bore. Relative motion among at least two of the members causes the inner surface to contact the outer surface, inducing a super-elastic activation in the shaft, simultaneously securing the members together in a fixed relative position. Preferably, the relative motion is axial, with respect to a longitudinal axis around which torque is being transmitted through the fixed assembly.
In one or more preferred embodiments of the invention, the contact established is a surface-to-surface contact that frictionally transmits an applied torque.
In another preferred embodiment of the invention, the female coupling member may be adapted for connection with a powered driving instrument or may be a fitting adapted to present a tool-bit. Similarly, the radially flexible sleeve may be adapted for connection with a powered driving instrument or may be a fitting adapted to present a tool bit.
In yet another preferred embodiment of the invention, the radially flexible sleeve member has a plurality of collet fingers, which preferably contact the shaft at discrete locations. It is further preferred that the super-elastic activation in the shaft occurs as a result of the discrete contact thereby changing the cross-sectional shape of the shaft, which is generally non-circular, e.g., polygonal, in a further preferred form. In still another preferred embodiment of the invention, the through bore of the radially flexible sleeve member has a generally non-circular, e.g., polygonal cross-section. Alone or in combination with the immediately aforesaid feature, the shaft may be generally cylindrical and deformed, e.g., polygonally, by compression against the through-bore.
In still another preferred embodiment, the shaft has a tubular shape defining a cannulation. More preferably, the tapered bore of the female coupling member, the through-bore of the sleeve member and the cannulation of the shaft member are concentrically aligned with respect to a longitudinal axis around which torque is transmitted through the fixed assembly, further admitting passage of a guide wire through the members.
In one of its aspects, a torque-transmitting assembly of the present invention has a female coupling member defining a shape with a tapered bore and a radially flexible sleeve member having a tapered exterior surface, received within the bore. The sleeve has an inner surface defining a through-bore and a plurality of collet fingers. An elongated tubular shaft member has a cannulated structure and is made of super-elastic alloy, defining an outer surface that is received within the through-bore. Relative axial motion among at least two of the members causes the collet fingers to contact the shaft at discrete locations inducing a super-elastic activation in the shaft that changes the cross-sectional shape of the shaft, simultaneously securing the members together in a fixed relative position by surface-to-surface contact that transmits torque through the assembly. Preferably, the tapered bore of the female coupling member, the through-bore of the sleeve and the cannulation of the shaft are concentrically aligned with respect to a longitudinal axis around which torque is transmitted through the fixed assembly, further admitting passage of a guide wire through the members. In a preferred form, the shaft is generally cylindrical and is deformed polygonally by compression against the through-bore.
In another of its aspects, a surgical device of the present invention includes a torque transmitting coupling assembly, which has a female coupling member defining a shape with a tapered bore and a radially flexible sleeve member having a tapered exterior surface, received within the bore. The sleeve has an inner surface defining a through-bore and a plurality of collet fingers. An elongated shaft member made of super-elastic alloy has an outer surface that is received within the through-bore. Relative axial motion among at least two of the members causes the inner surface to engage the outer surface, inducing a super-elastic activation in the shaft, simultaneously securing the members together in a surface-to-surface contact that frictionally transmits an applied torque around a longitudinal axis of the assembly, securing the members together in fixed relative position. The through bore of the radially flexible member preferably has a generally polygonal cross-section. The female coupling member may be adapted for connection with a powered driving instrument or it may be a fitting adapted to present a tool-bit. Preferably, the tapered bore of the female coupling member, the through-bore of the sleeve and the cannulation of the shaft are concentrically aligned with respect to a longitudinal axis around which torque is transmitted through the fixed assembly, further admitting passage of a guide wire through the members.
In yet another of its aspects, a flexible surgical reamer of the invention is described, including an elongated tubular shaft made of super-elastic alloy and defining an outer surface with a cannulated passageway extending along a first axis, the shaft having a driven end and a driving end opposite the driven end. The reamer has a first coupling assembly that includes a drive fitting located at the driven end, defining a shape with a first tapered first bore, also a radially flexible sleeve having a wall with a tapered exterior surface, received within the bore. The sleeve has an inner surface defining a through-bore and a plurality of collet fingers. Relative motion among at least two of the shaft, fitting and sleeve causes the through bore to contact the shaft, inducing a super-elastic activation in the shaft, simultaneously securing the shaft, fitting and sleeve together in fixed relative position. The reamer has a second coupling assembly that includes a fitting defining a shape with a second tapered bore. A tool-bit has a second axis and presents a first mating interface surface. A tool has a tool axis and presents a second mating interface surface adapted for receptive complemental facing with the first mating interface surface. A deformable tongue made of super-elastic alloy, is located adjacent the driving end, and is preferably formed from the shaft. Relative motion between the tool-bit and tool slides the first and second mating interface surfaces sideways into juxtaposition, with the first, second and tool axes aligned with one another.
An advantage of the present invention is a coupling assembly for an elastic tube that transmits torque without creating stress risers. More specifically, there is provided a reliable means of connecting various types of tool heads to an elastic tube such that significant torque may be transmitted without raising internal stresses to dangerous levels. Such an advantage is particularly beneficial in surgical devices that require relatively high torque-transmission, while demanding the utmost safety in operation, e.g., flexible-reaming systems.
Another advantage is the ready assembling and disassembling of the present couplings, due to the properties of the preferred nitinol alloy.
Other objects and advantages will become apparent to those skilled in the art, upon reviewing the Figures of the Drawings, in conjunction with the Detailed Description set forth further below, wherein references to numerals corresponds to like references in the Drawings.